This invention relates to tubular food casings of the type commonly used to encase food products such as sausages. Such casings are often provided to the meat packer in the form of shirred strands, i.e. tubular food casing which is folded and compressed along its longitudinal axis so as to provide from 25 to 200 length units of uncompressed casing per single length unit of the shirred strand.
Such strands have a hollow longitudinal bore which can be placed over a stuffing horn of a food stuffing machine and filled with the desired food product such as sausage meat. During the stuffing operation food casing is "deshirred" from the shirred casing strand until essentially all of the tubular film contained in the shirred strand has been deshirred and stuffed. In order for the stuffing operation to proceed as described above, the leading end of the tubular food casing must be closed in some way. In the absence of such a closure, food product would simply pass completely through the strand, be spilled and lost without deshirring the casing. Numerous types of end closures have been tried for this purpose such as ties, knots, clips, twisted arbor closures, e.g. as described in U.S. Pat. No. 4,536,175, and axially compressed end closures, e.g. as described in U.S. Pat. No. 4,551,370. A problem encountered with end closures has been that gas may become trapped between the food product and the end closures. In order to alleviate that problem arbor end closures have been provided with vents which are easily formed as the twisting arbor is removed from the end closure. Such a vented arbor (gripper) type end closure may for example be seen in U.S. Pat. No. 5,088,956. The vents in the arbor type end closures have been beneficial in permitting gas to escape from the food casing during the stuffing operation. Unfortunately arbor type end closures have had other disadvantages. In particular arbor type end closures generally do not tightly contact the sidewalls of the bore along the entire length of the twisted plug forming the closure and can thus accommodate less force than compression type end closures before blowing out thus creating unsanitary conditions, manufacturing down time and lost food product. Furthermore arbor type end closures tend to be conical in shape and can sometimes be forced off center by impinging food product thus causing an asymmetrical end on the initial stuffed food product and also possibly closing any existing vent or causing a failure of the end closure and subsequent loss of food product and equipment down time.
Up to now compression type end closures have not been provided with vents which is due both to the lack of recognition that they could be because the act of compression would close any formed vent and further without twisting, even if a vent could be formed, it would tend to collapse because of stress applied against it by surrounding compressed casing. In addition, compression type end closures have not been forward strippable, i.e., it has not been possible to easily remove meat product through the end having the end closure by unraveling the end closure.
A further disadvantage of both arbor type end closures and compression type end closures is that the force to push out the end closure is not consistent from one strand to another. This makes it difficult to manufacture a consistent stuffed casing end product.